Hydrogenation of aromatic rings having two or more amino groups bound to the aromatic ring produces amino-substituted hydrogenated rings, such as cycloaliphatic di- or polyamines, which are useful chemical intermediates, e.g., for further reaction with epoxides or isocyanates. The amino groups may also be converted to isocyanate groups e.g. via reaction with phosgene or through known phosgene free methods. The resulting cycloaliphatic di- or higher functional isocyanates may also be used as monomers for making polymers, in particular, polyurethanes.
Until now, many polyurethane materials are made based on aromatic di- and polyamines as starting materials. A disadvantage of using aromatic di- and polyamines is that the amines, the corresponding aromatic di- and polyisocyanates and the resulting products darken with time and gradually turn brown or black e.g. due to oxidation upon contact with air. Products derived from aliphatic and/or cycloaliphatic isocyanates behave differently and are known as “light stable” after conversion to polyisocyanates or polyurethanes. The stability of compounds derived from di- and polyamines may be improved by hydrogenating the aromatic ring to the corresponding cycloaliphatic di- and polyamines. Known heterogeneous hydrogenation catalysts, however, lack in sufficient activity for the core-hydrogenation of amino-substituted aromatic rings and lack in chemoselectivity towards primary amines. Frequently observed side reactions include the condensation of primary amino groups to secondary or tertiary amino groups and/or the hydrogenolytic cleavage of the C—N bond between the aromatic ring and the amino group.
Moreover, many applications of di- and polyamines, such as for making active ingredients in the pharmaceutical industry or use as a monomer for making polymers, require a high degree of stereomeric selectivity with regard to the position of the substituents relative to each other on the hydrogenated ring, such as the resulting cycloaliphatic ring. When incorporated into a polymer chain, e.g., by conversion to the corresponding diisocyanate and subsequent reaction with a diol, trans-1,4-diaminocyclohexane results in a polymer chain with linear connections, while cis-1,4-diaminocyclohexane results in a polymer chain with non-linear connections. Materials made from polymers with such linear or non-linear connections display different macroscopic properties, such as a different glass transition temperature. The properties of materials made from diastereomeric mixtures of 1,4-diaminocyclohexanes vary in their properties with the content of the different diastereomers. Therefore, control of the ratio of the diastereomers is essential for controlling the properties of such materials. Diastereomers also may have different reactivities, so that compositions having a high proportion of one diastereomer can improve the uniformity of reaction rates when used in subsequent reactions, such as polyaddition or phosgenation reactions.
1,2-Diaminocyclohexanes with two amino groups attached to the same cycloaliphatic ring system in the 1,2-positions, as represented by formulas (I), which contain a high proportion of amino groups in cis position to each other, are advantageous for the reaction with phosgene. This is because the cis isomers are less prone than the trans isomers to form cyclic urea compounds, which are undesired by-products in the synthesis of isocyanates.

1,3-Diaminocyclohexanes with two amino groups attached to the same cycloaliphatic ring system in the 1,3-positions, as represented by formulas (II), which contain a high proportion of amino groups in trans position to each other are advantageous for the reaction with phosgene. This is because the trans isomers cannot form cyclic urea compounds, which are undesired by-products in the synthesis of isocyanates.

1,4-Diaminocyclohexanes with the two amino groups attached to the same cycloaliphatic ring system in the 1,4-positions, as represented by formulas (III), which contain a high proportion of amino groups in trans position to each other are advantageous for the reaction with phosgene. This is because the trans isomers cannot form cyclic urea compounds, which are undesired by-products in the synthesis of isocyanates.

Among the methyl substituted 2,4-diaminocyclohexane derivatives represented by formulas (IV) trans-cis-2,4-diamino-1-methyl-cyclohexane and cis-trans-2,4-diamino-1-methyl-cyclohexane, whereby cis and trans each refer to the position of the respective amino group relative to the methyl group, obtained by hydrogenating 2,4-diaminotoluene (2,4-TDA), are particularly advantageous for phosgenation, since these diastereomers do not form cyclic compounds, and trans-trans-2,4-diamino-1-methyl-cyclohexane, another diastereomer obtained by hydrogenating 2,4-TDA, is considered acceptable, since this diastereomer is less prone to form cyclic compounds, while cis-cis-2,4-diamino-1-methyl-cyclohexane is particularly prone to forming cyclic urea compounds during phosgenation.

Analogously, among the methyl substituted 2,6-diaminocyclohexane derivative as represented by formulas (V), cis-trans-2,6-diamino-1-methyl-cyclohexane, obtained by hydrogenating 2,6-diaminotoluene (2,6-TDA), is particularly advantageous for phosgenation, since this diastereomer does not form cyclic compounds, and trans-trans-2,6-diamino-1-methyl-cyclohexane, another diastereomer obtained by hydrogenating 2,6-TDA, is considered acceptable, since this diastereomer is less prone to form cyclic compounds, while cis-cis-2,6-diamino-1-methyl-cyclohexane is particularly prone to forming cyclic urea compounds during phosgenation.

The phosgenation of such cycloaliphatic 1,2- or 1,3-diamines is known, see EP-B 1078918. Independent from ease of phosgenation, the preferred diastereomers are advantageous for the modification (oligomerisation) of the synthesized diisocyanates.
The use of conventional catalysts for the hydrogenation of 2,4-TDA or 2,6-TDA tends to provide diastereomer mixtures having a high proportion of undesired isomers, such as the cis-cis isomer.
An example of a hydrogenation of aromatic amines is given in EP 0 630 882 A1. Ring hydrogenation is effected by reacting the aromatic amine with H2 in the presence of a catalyst comprising Rh on kappa-alumina. Also claimed is a process for hydrogenating crude methylene-dianiline (MDA) to produce 4,4′-methylene-dicyclohexylamine (PACM) in the presence of a 7:1 mixture of a Rh catalyst and a Ru catalyst, where at least the Rh catalyst is supported on kappa-alumina. The obtained product comprised 1 to 3% deaminated products and 13 to 19% secondary amines. It would be desirable to have access to catalytic systems having a lower rhodium content and displaying a higher reaction rate also for less reactive aromatic amines.
An example of the use of additives in the hydrogenation of aromatic amines is given in Kim et al., J. Mol. Catal. A: Chem. 132 (1998) 267-276. The influence of added alkali metal salts on the performance of ruthenium catalysts has been examined. It was found that the cations of the metal salts interac with the supporting material. NaOCH(CH3)2 was identified as the active species. The product obtained in the hydrogenation of methylene-dianiline (MDA) and 1,4-phenylenediamine comprised 2 to 99% of products with partially hydrogenated aromatic rings, 1 to 5% deaminated products, as well as 2 to 7% secondary amines. It would be desirable to have access to catalytic systems having an improved reaction rate also for less reactive aromatic amines.
US 2010/292510 A1 relates to a process for preparing cycloaliphatic amines comprising performing hydrogenation of corresponding aromatic compounds with hydrogen-comprising gas at a temperature of from 30 to 280° C. and a pressure of 50-350 bar, in the presence of ruthenium catalysts, and from 1% by weight to 500% by weight, based on the catalyst (calculated as elemental ruthenium (Ru)), of suspended inorganic additives.
U.S. Pat. No. 5,214,212 teaches the addition of metal salts as promoters in a process for hydrogenating aromatic amines. According to the disclosure, the addition of promoters leads to an improvement in the reaction rate and to a reduction in by-product formation. To maintain high activity of the catalyst system in the hydrogenation process, a transition and/or lanthanide metal salt promoter is added to the reaction system in an effective amount to increase the hydrogenation rate, eliminate the induction period of the hydrogenation reaction, and decrease the amount of higher boiling by-products. By way of illustration, an effective amount of the transition or lanthanide metal salt promoter is in the range from about 0.1% to about 15% by weight based on the starting aromatic amine. The preferred range is from about 0.3% to about 10.0%. These metal salt promoters can be used alone or in combination with other additives. Counter-ions such as the sulfate and phosphate can be used because they do not have non-bonded electrons on the sulfur and phosphorus, respectively. Thus, ferrous and cerous sulfates (either as the anhydrous salt or as a hydrate) are illustrative. Other anions that satisfy these criteria such as carboxylates (e.g. acetates) can be used.
U.S. Pat. No. 4,448,995 teaches a process for the catalytic hydrogenation of di(4-aminophenyl)methane to a liquid di(4-aminocyclohexyl)methane containing from 15 to 40% by weight of the trans-trans isomer comprising hydrogenating di(4-aminophenyl)methane at a hydrogen pressure of at least 500 psi and at a temperature of from 100 to 300° C., in the presence of a ruthenium catalyst supported on an inert carrier, said catalyst being moderated with from 65 to 700% by weight, based on the weight of the ruthenium, of a compound selected from the group consisting of nitrates and sulfates of alkali metals and alkaline earth metals. According to one embodiment, the catalyst is moderated with a compound selected from the group consisting of lithium nitrate and magnesium nitrate.
U.S. Pat. No. 6,075,167 relates to a method of preparing cycloaliphatic diamines by hydrogenating an aromatic diamine in an organic solvent in the presence of a supported ruthenium catalyst, wherein a metal nitrite is used as a catalyst promoter. In one embodiment, the metal nitrite is selected from the group consisting of Ba(NO2)2, NaNO2, KNO2 and AgNO2.